Oriented blends of ethylene polymers and petroleum waxes and process for preparing same



United States Patent 3,502,764 ORIENTED BLENDS OF ETHYLENE POLYMERS ANDPETROLEUM WAXES AND PROCESS FOR PREPARING SAME John P. Tordella,Wilmington, Del., assignor to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware No Drawing. Filed May 31,1966, Ser. No. 553,631 Int. Cl. D01f 7/02; C08f 3/04 US. Cl. 264-210 6Claims ABSTRACT OF THE DISCLOSURE This invention relates to novelpolymeric products and a process for preparing such products. Moreparticularly, the invention relates to oriented, self-supportingpolymeric structures comprising blends of ethylenic polymers andpetroleum wax and a process for orienting such structures.

BACKGROUND OF THE INVENTION Orientation of films and filaments and theattendant increase in strength properties is well known. In the drawingprocess, it is the usual practice to raise the temperature during thedrawing step. However, a much greater degree of orientation is inducedby drawing at temperatures below the melting point of the compositioncomprising the article to be drawn than above. If the polymeric materialhas a fairly definite melting point, no substantial problems areencountered. This may not be true, however, in the case of blends of twoor more components having significantly different melting points.Substantial orientation of the lower melting components is not usuallyobtained at draw temperatures above their respective meltingtemperatures.

DESCRIPTION OF THE INVENTION Surprisingly, it has been found that by theprocess of this invention oriented structures comprised of ethylenicpolymers blended with petroleum wax can be prepared which exhibitsubstantial orientation of both components of the blend.

In accordance with this invention, these oriented structures areprovided by first forming a shaped article of a homogeneous polymer-waxblend, heating the shaped article to a temperature above the meltingpoint of the wax but below the melting point of'the polymericcomponent-and then drawing the article while the wax is still in themolten state. Thereafter, the drawn article is cooled to roomtemperature. Quite unexpectedly, the drawn article produced shows (bycharacteristic X-ray patterns) molecular orientation in the direction ofdrawing of both components even though the structure has been drawn at atemperature at which the wax is molten and unoriented. Drawing increasesthe tensile strength of the article, and whereas only limited drawingcan be accomplished at temperatures below the melting point of the wax,very large amounts of draw can be effected by following the teaching ofthis invention.

In practicing this invention, the components from which the article isprepared are so selected that the difference between the melting pointof the polymer and the wax is at least 10 C. Generally the difference inmelting point will not be greater than about 90 C., however, theultimate limiting factor will be the temperature at which the wax wouldbe degraded by heating to the selected drawing temperature. Thisdifference in melting points is referred to herein as the temperatureinterval. Melting points are defined herein as the temperatures at themaximum temperature difference 3,502,764 Patented Mar. 24, 1970 betweenthe wax or polymer specimen and an inert reference material when bothare heated in a differential thermal analyzer in accordance with theprocedures described by B. Ke in Organic Analysis volume 4,Interscience, New York (1960). These peak temperatures are somewhatlower than the temperature at which all crystallinity disappears.Relative to waxes, the melting point is the peak temperature relative tothe disappearance of the highest melting crystalline phase versus thepeak which may accompany a lower temperature crystalline phase change.

The polymeric components useful in this invention are known polymers andcopolymers of ethylene of moderate to high molecular weight, i.e.,having a melt index of less than 10 and preferably from about 0.001to 1. The polymers exhibit ethylenic crystallinity (as determined bystandard X-ray diffraction techniques) and generally contain at least?mole percent of ethylene. In addition to ethylene homopolymer,copolymers containing up to 20 mole percent of any monomer containingwolefinic unsaturation capable of coploymerizing with ethylene toprovide products which have a suitable melt index, contain residualethylenic crystallinity, and are miscible in the wax component aresatisfactory. AmOng the wide variety of comonomers are vinyl acetate,alkyl acrylates, u-olefins having from three to eight carbon atoms andunconjugated diolefins having five to eight carbon atoms. Blends of twoor more of the polymers may be used.

The wax component of the blend is selected from paraffin,semi-microcrystalline and microcrystalline waxes or blends thereof andwill be referred to herein as petroleum waxes. Paratfin wax is a mixtureof solid hydrocarbons derived from the overhead wax distillate fractionobtained from the fractional distillation of petroleum. It is a hard,translucent, usually colorless material having a melting point of aboutto F. Microcrystalline wax is obtained from the nondistillable stillresidues from the fractional distillation of petroleum. It differs fromparaflin wax in that it contains significant quantities of branched andcyclic hydrocarbons. The microcrystalline wax may be'considerably moreplastic than paraffin wax. The semimicrocrystalline waxes haveproperties which generally fall in a range between those of the paraffinand microcrystalline waxes. A single wax or blend of two or more waxesmelting between about 50 C. and 80 C. may be used in preparing thepolymer-wax blends. The waxes must, of course, blend, i.e., be misciblewith the polymer at temperatures above its melting point.

The polymer-wax blends may be prepared by known processes. Blending maybe accomplished by heating and stirring the components or by mixing inheavy duty mixers such as rubber rolls, sigma blade mixers or screwextruders. In preparing the blend from about 10% to 50% by weight of thepolymer is used with about 90% to 50% by weight of the wax. Generally,20% to 40% by weight of polymer is used. The amount of polymer requiredto provide a given degree of orientation in the final article decreasesas the melt index of the polymer is decreased. Minor amounts of otheringredients such as stabilizers, pigments and fillers may be included inthe blends.

Shaped structures comprised of the copolymers-wax blends may be preparedby well known extrusion and molding techniques. The shaped articles arethen drawn in accordance with this invention two or more times theiroriginal unit length. Drawing may be monoor biaxial. Biaxial drawing maybe accomplished by widening a sheet continuously while stretchinglongitudinally, by expanding a tube while drawing it axially or bymolding operations wherein the area of a film or sheet of the blendedcomponents is increased by extension. The drawing must, of course, becarried out within the aforementioned temperature limitations.

This invention will be further illustrated by the following examples inwhich parts and percentages given are by weight unless otherwisespecified.

EXAMPLES In the following examples polymer-wax blends of the specifiedingredients are prepared by stirring the polymer and wax in a beakerheated on a hot plate at about 300 F. until partial solution isachieved. Final mixing is accomplished using a heated (about 300 F.) tworoll mill. Films about inch thick of the blend are formed by compressionmolding. The films are drawn at the temperatures indicated in the tablewhich follows. The melt index of samples is determined by ASTM D 123857Tusing a temperature of 190 C. and load of 2160 grams. Each of thepolymers exhibited typical ethylenic crystallinity as determined bystandard X-ray difiraction techniques.

4 from about 90% to 50% by weight of petroleum wax, said polymer andsaid wax having a temperature interval of at least 10 C., forming ashaped article from said blend, heating said shaped article to atemperature above the melting point of said wax but below the meltingpoint of said polymer until said wax becomes molten, drawing said shapedarticle while the wax is in the molten state at least two times itsoriginal unit length or area and thereafter cooling the drawn article toroom temperature.

2. The process of claim 1 wherein said polymer has a melt index from.about 0.001 to 1, said polymer is present in said blend in an amountfrom about 20% to 40% by weight, and said wax is a petroleum wax havinga melting point from about 50 C. to 80 C.

3. A process according to claim 1 wherein the melt index of said polymeris from 0.001 to 1, said polymer is present in an amount from about 20%to 40% by weight and the temperature interval is from 10 C. to 90 C.

4. A process according to claim 3 wherein said polymer is polyethylenehaving a melting point of about 134 C.

TABLE Data for Oriented Film Orientation Conditions Polymer Wax BlendUnoriented Polymer] Film, Tenslle Draw Ratio Tensile Melt M.P. M.P. Wax(wt. Strength at Temp. Strength at Elongation Example No. Type Index C.)Type 0.) percent Break 8 (p.s.i.) C.) Umaxlal Bmxial Break 5 (p.s.i.)(percent) E/P 1 0. 008 118 A 64 40:60 917 12 2, 752 117 El 3 0. 001 119A 64 40:60 1, 186 10. 5 4, 433 155 E/HD 4 0. 004 103 A 64 :70 6 2, 631216 Elli-1 1. 4 90 A 64 :60 1, 486 13. 3 2, 892 230 E 0. 02 134 B 7 6840:60 1, 334 13 000 8 E 0. 02 134 A 64 20:80 525 13. 3 2, 800 164 E 0.02 134 A 64 30:70 1, 036 2. 6 1, 244 875 E 0. 02 134 A 64 30:70 1, 03610. 4 4, 227 143 E 0. 02 134 A 04 30:70 1, 030 28. 2 0, 075 158 E 0. 02134 A 04 40:60 1, 388 2. 9 2, 110 460 E 0. 02 134 A 64 40:60 1, 388 8. 10, 000 225 E 0. 02 134 A 04 40:60 1, 388 28. 2 12, 250 130 lEthylene/propylene copolymer containing 21% by weight propylene.

2 "Aristowax 143-150, Witco Chemical C0.'s parafiin wax.

B EthyleneIhexene-l copolymer containing 11 mole percent hexene-l.

Ethylene polymer containing 0.5% by weight (maximum) butenc-l.

of area of minimum original cross-section at the moment of rupture ofthe test specimen (ASTM 7 "Suncco mierocrystalline wax. 5 Tensilestrength at break-tensile loads per unit 9 Ratio of thickness of filmbefore to that after drawing.

The drawn samples are each examined by the usual K-ray techniques todetermine the extent of orientation )f the blend components. In allcases the drawn article ahows (by characteristic X-ray patterns)molecular orien- :-ation in the direction of drawing of both components:ven though the article is drawn at a temperature at which :he wax ismolten and unoriented.

It will be apparent from the foregoing examples that products preparedaccording to this invention exhibit greatly increased tensile strengthwith considerable elongation prior to rupture. The strength increaseswith in- :reasing amount of polymeric component and with in- :reasingdraw. An unexpected advantage resides in bondng films of this inventionto themselves or to other maerials such as paper, aluminum, iron andglass .by simply reating the oriented structure to a temperature withinthe emperature interval. The products of this invention also :xhibitgood energy absorption on impact. They are also lseful in applicationswhere shrinkage of a film is desired .ince the unrestrained film shrinkwhen heated above the melting point of the wax component.

Since many diiferent embodiments of this invention may be made withoutdeparting from the spirit and scope hereof, it is to be understood thatthe invention is not imited by the specific illustrations except to theextent lefined in the following claims.

What is claimed is:

1. A process for preparing an oriented article which hows bycharacteristic X-ray patterns molecular orientaion in the direction ofdrawing which comprises blending 'rom about 10% to by weight of anorientable :thylene polymer having a melt index of less than 10 withUNITED STATES PATENTS 3,376,244 4/ 1968 Rundle. 2,920,349 1/ 1960 White.3,210,305 10/1965 Coenen 260285 3,243,396 3/1966 Hammer. 2,980,964 4/1961 Dilke. 3,182,033 5/1965 Gregorian. 3,261,903 7/1966 Carr 264-2103,299,194 1/1967 Golike 264-210 3,223,764 12/1965 Kahn 264*210 FOREIGNPATENTS 937,807 9/ 1963 Great Britain.

MORRIS LIEBMAN, Primary Examiner P. R. MICHL, Assistant Examiner

